1. Field of the Invention
The present invention relates to an X-ray computed tomography apparatus with a heat emission system that emits heat regenerated in resistors and further relates to the heat emission system.
2. Discussion of the Background
Recently, medical diagnosis devices have been improved outstandingly. Particularly, various techniques have been introduced in the field of an X-ray computed tomography apparatus (hereinafter referred to as a CT apparatus), which uses an X-ray to tomograph an examination object or a patient (hereinafter referred to as a specimen). In addition, a tomography time has been reduced more than before.
In such a technical innovation, an issue that is always considered is how to emit heat caused collaterally in the CT apparatus. It is a fact, however, that the heat needed to be emitted increases as the CT apparatus is improved. Therefore, this is one of several serious problems related to development of a further improved CT apparatus as well as for a current CT apparatus.
One well-known type of heat, which is caused inside the CT apparatus, is heat generated by regenerative resistors. In the CT apparatus, a motor, such as, for example, a direct drive motor or a rotation servo-motor, drives a rotation ring that rotates for tomographing a specimen. When a rotation speed of the rotation ring is reduced, back electromotive force energy is generated. The regenerative resistors are provided for converting the back electromotive force energy into heat energy.
Therefore, when acceleration and deceleration of the rotation speed are alternately repeated so often by the motor, the regenerative resistors sometimes reach a high temperature (e.g., 70° Celsius). Such repetition may occur, for example, when a lot of specimens are continually tomographed or when a field engineer implements a maintenance service on the CT apparatus.
One solution for the above issue is an increase of the number of the regenerative resistors. Other proposed solutions are described below as examples.
One type of the CT apparatus has an orthogonally shaped gantry in a view from a front side of the CT apparatus. In such a CT apparatus, one or more regenerative resistors are provided at a top of the gantry so as to easily emit heat from the regenerative resistors. Further, the regenerative resistors contact with a sheet metal provided in the gantry so as to let out the heat through the sheet metal. This type of CT apparatus may be replaced by the following type of CT apparatus, considering a psychological burden on the specimen.
Another type of CT apparatus has a gantry with a top in a shape of an arc so as to present a moderate impression. This configuration may reduce the discomfort experienced by a specimen. In such a CT apparatus, it is difficult to keep an enough space to provide the regenerative resistors at a top of the gantry. Therefore, the regenerative resistors are often provided at one or more sides of the CT apparatus.
In this type of CT apparatus, a fan or the like is additionally provided and used to guide heat caused by the regenerative resistors to the outside of the CT apparatus. For example, Japanese Patent Application Publication No. PH9-276262 describes a CT apparatus, which has a suction opening at an upper side of a gantry opening and a cooling fan at a top of the gantry. Accordingly, an air stream is caused through the suction opening and the cooling fan, which results in heat emission.
A further example of using a fan is described in Japanese Patent Application Publication No. PH9-56710. In this example, a CT apparatus includes a supporting member with a plurality of blade members. These blade members are rotated with a rotation ring so as to send air to emit heat inside the CT apparatus. Similar to the example of Japanese Patent Application Publication No. PH9-276262, this example emits heat by ventilating an inside of the CT apparatus.
Still further, a CT apparatus described in Japanese Patent Application Publication No. P2002-336236 includes a regenerative resistor unit and a ventilation fan. The regenerative resistor unit is provided inside a gantry. The ventilation fan provides a bed where a specimen lies with heat caused by the regenerative resistor unit. This helps to warm the specimen. Also similar to the example of Japanese Patent Application Publication No. PH9-276262, this example emits heat by using an air stream.
As described above, various techniques have been introduced for solving the heat issue. On the other hand, tomography time reduction is still being challenged for reducing more the discomfort and X-ray exposure of the specimen.
This challenge means reduction of scanning time. For the reduction of the scanning time, it is necessary to rotate a rotation ring, which is used for tomography, much faster. Since the rotation ring is driven by the motor, the motor is required to be accelerated and decelerated more quickly. This results in generation of a larger amount of regenerative energy, compared to the heat generated before. Accordingly, a larger amount of heat energy is generated by regenerative resistors.
Such a large amount of heat energy cannot be adequately released by the above-described techniques disclosed in the Japanese Patent Application Publications. If the heat emission does not function well, the temperature goes up inside the CT apparatus, so that defective performance may be caused in various precision devices provided in the CT apparatus.
As the above-described CT apparatus having a top in a shape of an arc, regenerative resistors may be provided at sides of a CT apparatus. In this case, if a doctor or a radiological technologist passes by the CT apparatus for taking care of a specimen lying on a bed, the doctor or the radiological technologist may happen to touch the regenerative resistors (or a body part of the CT apparatus incorporating the regenerative resistors) by accident and be burned. Similarly, a field engineer may happen to touch the regenerative resistors by accident during maintenance service and be burned.
If action is taken for safety in the above burning case, the CT apparatus may require a complex configuration and/or a high cost in manufacture. For example, the CT apparatus may need to include a function of effectively lowering the temperature of the regenerative resistors. Further, the CT apparatus may need a function of avoiding heat conduction to a body surface of the CT apparatus.